In a known electric power conversion device including reactors, power modules and capacitors, a cooling water passage is formed in a specific area of a bottom plate of a case, and the reactors and the power modules are positioned on the part of the bottom plate corresponding to the cooling water passage while the capacitors are placed on other part of the bottom plate. See JP2017-135901A. The part of the bottom plate where the cooling water passage is absent has a relatively low upper surface so that the vertical dimension of the space defined above such a part can be maximized.
However, according to the electric power conversion device disclosed in JP2017-135901A, the capacitors are too remotely positioned from the cooling water passage to be adequately cooled. Also, because the reactors, the power modules and the capacitors are positioned on a single plane without any overlap, the area of the necessary floor space (footprint) is undesirably great.